Caption: Following the International Astronomical Union's 2006 formal definition of what consitutes a planet, Pluto was reclassified as a dwarf planet, and as such is the second most massive after Eris. It is the largest body in the Kuiper Belt and the tenth most massive object in the Solar System. Pluto has five known moons, the largest being Charon (seen here in the sky) with a diameter just over half that of Pluto. Although officially classified as a moon of Pluto, some regard Pluto and Charon as a binary planet system; the system is barycentric, meaning the centre of mass of the two bodies lies outside either individual body. The four other moons are Styx, Nix, Kerberos and Hydra. The Pluto System orbits the sun once every 248 years, with a highly inclined (17 degrees to the ecliptic) and highly eccentric (elliptical) orbit. The planet is largely comprised of rock and ice.